OK, guess it's time to ease in here.
Some very good thoughts so far. Glad you guys zeroed in on the distinction between an up movement of the CM that results from the lateral turn force driven movement of the CM, and an up movement born of aggressive extension, and resulting in an unweighting of the skis. Nolo, I too like that relaxed and ready neutral position. Bud, good definitions. And, skiingman, stay tuned. I'll try to answer your "why" question.
*******************THE HISTORY OF UP
Back in the days when Ruedi was writing Pianta Su, a strong up/extension move was considered state of the art technique, and for good reason. Straight skis demanded the use of a technique very different from that of shape skis today.
During the days of straight skis, body positions were generally quite upright with the CM kept more laterally more over the feet.http://www.olympic.org/uk/utilities/multimedia/photo_uk.asp?EntIdProv=804&EntId=1890&LinkName=ING EMAR+STENMARK&Direct=0
Why, you ask? Well, it all had to do with sidecut. Because of the lack of sidecut in the straight skis of old, carved turns were very large radius. The resultant centrifugal forces those turns produced were very low in comparison to the external forces produced by the shape skis of today. As such, the CM had to be kept very much over the skis to maintain balance on the outside ski.
To do that, racers employed knee angulation so they could put their outside ski on a high edge angle, yet not have to drop the hip into the turn and lose their outside ski balance (see above photo link). Yes, it was a structurally weak position, but it was the only option their skis afforded them.
Because they had to be so upright and over their skis through the body of their turns, it was necessary to extend through the transitions, to eliminate the often severe knee angulation of the prior turn, and get tall and prepared for the efficient initiation of the new turn.
Coupled with that was the issue of turn radius. While carving was considered by racers even back then to be the fastest way to travel through a turn, the small amount of sidecut their skis possessed limited how sharply they could change direction by means of carving alone.
This reality dictated that racers needed to find other ways to supplement carving when the direction change required was beyond the capacity of the ski to achieve via it's sidecut. There were two primary means of doing that, and both were founded on an aggressive, extending up move.
The first was a traditional redirection of the skis at the top of the turn prior to initiating the carve. Because racers did not have the luxury of starting a new turn by crossing over and diving to the inside of their skis with their CM, then waiting for massive forces to emerge (as shape skis generate today) to provide instant lateral balance for them, they had to go into the new turn in an upright position. This necessitated an up unweighting to facilitate the redirecting pivot and put them in a good upright position for the post pivot edge engagement.
The second means of carve supplementation was a post carve diverging step. This is the move that Stenmark made a career of.http://www.olympic.org/uk/utilities/multimedia/photo_uk.asp?EntIdProv=804&EntId=1884&LinkName=ING EMAR+STENMARK&Direct=0
The idea here was to execute progressive knee flexion through the body of the turn, then finish with an explosive extension, providing a powerful and speed generating forward projection onto a diverging old inside ski. It was called a skate step, or an inside/outside step (inside edge of old outside ski, to outside edge of old inside ski).
With it a skier could initiate a turn without any pivot, a true arc to arc transition, knee angulate the outside ski into a clean carve, then finish the turn with an angular step that could produce up to about 30 degrees of direction change. It was an up move that provided dramatic and effective results. Stenmark used it to collect 86 WC wins, and our own Epicski resident Debbie Armstrong used it to capture her Olympic Gold.BACK TO THE FUTURE